For decades, magnetic recording has been effected on magnetic tape. While a wide assortment of cartridges has been designed to house such tapes and protect them from damage, they all conform to certain established Technical Standards that assure that all cartridges in a particular class can be used in tape drives designed to receive such classes of cartridges. A popular magnetic tape cartridge which is often used for recording computer-generated data is the DLT-2000 Magnetic Tape Cartridge manufactured by Digital Equipment Corporation. This cartridge, shown in FIGS. 1 and 2, is designed to meet Standard ECMA-197, a technical standard set by the European Computer Manufacturers Association (ECMA) in December 1993. The title of this standard is "Data Interchange on 12.7 mm 112-Track Magnetic Tape Cartridges--DLT 2 Format."
Referring to FIGS. 1 and 2, the DLT-2000 cartridge comprises a box-like container 10 which is adapted to receive a spirally wound strip of magnetic recording tape. The cartridge includes square top and bottom walls, 12 and 14, respectively, each supporting flanges 16 which abut each other to define four side walls 18A-18D. The front side wall 18A enters the tape drive first and is provided with a pivotally mounted access door 20 through which the tape drive gains access to the magnetic tape within. The access door is mounted on the cartridge for pivotal movement about axis A. When the cartridge is not in use, the access door is in a cartridge-closing position, as shown in solid lines in FIG. 2. When the cartridge is being used, the access door is pivoted about axis A to an open position, as shown in phantom lines in FIG. 2. When the access door is opened, a tape drive mechanism can enter the cartridge and withdraw the free end of the tape within. To prevent the access door from swinging open when the cartridge is not in use, the door is spring biased towards its closed position, and a door locking member 22 is provided. Door-locking member 22 is slidably mounted on the door to move in a direction parallel to pivot axis A, and a coil spring S serves to urge the locking member in a downward direction, as viewed in FIG. 1, towards its door-locking position. In its door-locking position, a free end (not shown) of the locking member engages a slot (not shown) formed in the cartridge's bottom wall and thereby prevents relative movement between the door and the cartridge. In loading the cartridge into a conventional magnetic tape drive, a door-unlocking structure associated with the drive acts to apply an unlocking force on the locking member, causing it to move in an upward direction, against the force of spring S. Simultaneous with the application of the door-unlocking force, another force is applied to an edge 20A of the access door, causing it to pivot about axis A to its open position. Upon opening the access door in the manner described, a tape drive mechanism enters the cartridge, engages the free end of the tape, and extracts the tape from the cartridge for use. In use, the tape is commonly wrapped in a helical fashion about a drum where it is scanned by a pair of magnetic write/read heads.
Recently, with the advent of optical disk recording and the tremendous increase in data storage capacity it represents, considerable effort has been applied to the challenge of optically recording data on tape. A relatively early disclosure of an optical tape recording system is provided in U.S. Pat. No. 4,807,213, issued Feb. 21, 1989 to S. T. Chung et al. According to this disclosure, an optical tape recording medium is wrapped in a helical fashion about a "laser drum" containing a pair of semiconductor lasers. The laser drum operates to helically scan slanted data tracks the tape, in a manner similar to the scanning technique used in conventional magnetic video tape recorders, to optically record and/or reproduce data on the tape.
Optical recording tapes of the type considered to date typically comprise a relatively thin and flexible laminate composed of a base layer of polyethylene terephthalate (PET) or the like, and a plurality of other layers superimposed thereon, including subbing, reflective, optical recording and encapsulation layers, in that order. Optionally, a gas-trapping transparent membrane may be added to the top of the encapsulation layer to displace dust and dirt particles from the focal plane of the recording layer. See, e.g., the disclosure of the commonly assigned U.S. Pat. No. 5,215,808, issued in the name of J. A. Barnard. The overall thickness of the laminate is about 25 microns, and data is recorded on the tape by forming micron sized marks in the recording layer. Since any foreign material (e.g., dust or dirt particles) and scratches on the tape surface can occlude significant portions of the recording layer and thereby prevent data from being either recorded thereon or reproduced therefrom, special care must be taken in the optical tape drive to avoid such artifacts. This special care requirement usually translates to a tape handling path within the optical tape drive which significantly differs from that used in conventional magnetic tape drives. Whereas a magnetic tape drive can, owing to the robust nature of the magnetic recording medium and recording process, treat the magnetic tape in a relatively physical manner, using capstan drives and pinch rollers to push and pull the tape through the drive, an optical tape drive must interact with its recording medium far less aggressively. Thus, were an optical tape housed in a Standard ECMA-197 cartridge, such as that described above, mistakenly loaded into a magnetic tape drive, it is highly probable that the optical tape would be seriously damaged by the magnetic tape drive. Further, were an optical tape housed in such a cartridge, the tape could be easily damaged by air-borne dirt and dust particles inasmuch as the aforementioned forces required to open the cartridge's access door can be readily applied by hand by the cartridge user, even inadvertently.